The heroine is a legitimate daughter of the Prime Minister's family, and she has a brother who is also a legitimate daughter. The male protagonist, the emperor, made a marriage contract when he was the prince.
Even if the male protagonist becomes the emperor in the end, he will still be very kind to the female protagonist.
There may be some minor supporting characters in the middle who may poison the heroine, but they will always reconcile with the heroine and become sisters.
However, the heroine has always been in poor health, but after taking good care of herself, the hero and heroine gave birth to a child.
But when the heroine was giving birth, she left!
In the ending, the male protagonist had to find a replacement...
Concept: sweet and comforting